Waveguide coupled tuning of cavity resonators for klystrons



April 27, 1965 E. A. Asl-l 3,181,025

WAVEGUIDE COUPLED TUNING OF CAVITY RESONATORS FOR KLYSTRONS Filed Jan. 22, 1962 By/Z/ Ator e United States Patent O 3,181,925 WAVEGUEDE CUPLED TUNENG F CAW'EY RESNATGES FR KLYSTRNS Eric Albert Ash, London, England, assigner to international Standard Electric Corporation, New York, NSY., a corporation or" Delaware Filed San. Z2, i962, Ser. No. 167,510 Claims priority, application Great Britain, dan. 25, 195i,

2,995/ 61 Claims. (Cl. 3dS-#5.53)

The invention relates to the tuning of cavity resonators.

ln klystron devices for use in the millimetre wavelength range, the cavity resonator, the field of which interacts with the electron beam, becomes very small, so that it is virtually impossible to tune it directly by varying its dimens-ions or by the insertion of tuning screws. in order to couple such resonators to other circuits, however, it is common practice to provide an auxiliary resonator, coupled through a slot in the wall of the main resonator, and to tune the auxiliary resonator by mechanical means. Part of the auxiary resonator may be outside the evacuated part of the device; it may talie the form of a resonant length of hollow waveguide 1having a tapered matching section coupled at its end to the main resonator. Even though this auxiliary resonator is more accessible than the main lrlystron resonator, it may still be diicult, because of the small physical dimensions involved, to insert tuning screws or the like.V

In accordance with the present invention there is provided a tuning arrangement for `adjusting the resonant frequency of a length of hollow waveguide coupled to an aperiodic length of wavegui e through an inductive diaphragm, wherein a rod ot dielectric material is positioned for projection through the diaphragm into the resonant length ot waveguide by an adjustable amount, the other end ot the rod lying within the aperiodic length of waveguide. i

As applied to an electron velocity modulation device the invention provides such a device having a cavity resonator arranged for interaction between the electromagnetic field contained t erein and a stream or electrons entering therein, a resonant length of hollow waveguide coupled to the cavity resonator, a 'waveguide feeder coupled to the resonant length of 'waveguide through an inductive dia-v guide feeder.

Embodiments of the invention will be described with reference to the accompanying diagrammatic drawings in which:

FGS. l and 2 represent, respectively, a section through a diameter of a ldystron resonator and through thek asverse the axis ot the lrlystron resonator;

FIG. 2a is a cross-section of the waveguide showing a front view of the diaphragm;

FlG. 3 representsV a cross-section through the waveguide feeder in which is supported the dielectric rod;

FlG. 4 illustrates the arrangement of the micrometer tuning mechanism; and

PEG. 5 illustrates a way in which the dielectric rod may be shaped to provide also variable coupling between the tuned length of waveguide and the untuned waveguide fee er. i

Referring to FiGS. l and 2 of the accompanying drawings, part ot a reflex ldystron is indicated at l. The klystron has a solid copper block body portion of cylindrical form in which are formed two coaxial bores end-to-end separated by a thin septum 2. ln one bore a closure mem- .t .L internal dim.

3,l8l,025 Patented Apr. 27, 1965 ber la, shown as a separate member preferably pressure welded into the ldystron body, forms between its lower surface and the septum 2 a cavity resonator 3. The septum 2 and the closure member are centrally apertured to permit passage of an electron beam. ln the bore above the cavity resonator is situated a reflector electrode 4, while an electron gun 5 is mounted in the bore below the septum. A coupling waveguide'o, of tapering height and, in the embodiment illustrated, of rectangular cross-section, although it would also be of circular cross-section, is coupled to the resonator 3 through the side wall thereof. The tapering section is arranged to be half a guide wavelength long and, at its wide end, continues into a waveguide or" unitorm cross-section 6a. At the junction between the tapered and the uniform section a hermeticallyV sealing waveguide window '7 is provided. At a half guide wavelength from the window the waveguide is partially closed by an inductive diaphragm so that between the. resonator 3 and the diaphragm il a resonant length of coupling waveguide is provided which is a complete guide. wavelength long. ln a lrlystron made forruse in the regionY of 3.5 millimetres wavelength, the outer diameter of the blocl; or the hlystron l is 4.3 centimetres while the diami the esonator 3 is 4.4 millimetres; in so far as the ensions of the waveguide and resonator are concer led, the drawings of EGS. l and 2 are very roughly to scale. lt will be appreciated, therefore, that there is. very little space available in which to provide tuning elements or" a conventional nature.

In the embodiment shown, the inductive diaphragm 8 eparates the resonant length of waveguide from a continuing aperiodic length of feeder waveguide 9, of crosssection corresponding to that in the uniform portion of the resonant guide. A rod lll of dielectric material, preferably quartz, is situated in the waveguide 9; it is of rectangular cross-section andrhas a height in the working position approximately one half that of the waveguide; forward of the end remote from the diaphragm 8 the height tapers down to a negligible value at the end. The width of the rod, which is considerably exaggerated in FIG. 2, may be of the order of one tenthof the width of the waveguide. One endof the rod projects through the inductivediaphragm ii-this is of the symmetrical type comprising two opposing tins each joinedbetween top and bottom of thewaveguide and projecting from` the side wall towards the centre of the guide on each sideV of rod lil, as shown in FIG. 2a. The mean penetration of the dielectric rod into the resonant length of waveguide is one eighth of a guide wavelength. For a quartz rod having a dielectric constant of 5, with a ratio of the width of a waveguide to the width of the dielectric of l0 to 1, agvariation in the depth of penetration of about l millimetro is found to vary the frequency generatedV by the klystron by Vabout 10%.

The dielectric rod l@ is Vsupported hymeans not shown in FIGS. l and 2 from a pair of lugs 11 which project through a slot 12' in the broad side of the waveguide?.

FIG. 3 shows a means for supporting the dielectric rod lo in the waveguide 9. A rider 13 seats` around the outside of the waveguide and is carriedron a pair of spring loaded ball bearings 14. The lugs 11, which are cemented to the dielectric rod 10, are connected to a member 15 which is screwed onto the rider 11i.V The rider carries an extension, represented at 16, for actuation by a micrometre screw and return springftuning mecha K in which is also secured the waveguide 9. The head Z@ Y of the micrometre screw engages with extension .la of 3` rider 13a, which is held in contact therewith by means of a compression spring 21 engaging between the walls of the klystron and the opposite end of the extension 16.

If the penetration of the dielectric rod into the resonant length' of hollow waveguide is increased, the effective in which the dielectric rod 10', where it protrudesV through the diaphragm 8, is tapered in height so that as the rod is moved to the left further into 'the resonant length `of waveguide so the area of `dielectric occupying the aperture of the diaphragm increases. Such movement eects an increase in the coupling between the two waveguide sections on eitherv side of the diaphragm and hence, as the klystron is tuned to a lower frequencv, so the coupling is increased.

What is claimed is:

1. rA tuning arrangement for a resonant length of hollow rectangular waveguide coupled to an aperiodic rectangular waveguide feeder comprising an inductive coupling diaphragmextending symmetrically into the waveguide and positioned across the junction of the two waveguide sections, a rod of dielectric material having one end positioned within said feeder and the other end projecting through the diaphragm into said resonant length `and meansfor adjusting the amount of penetration of the rod into the resonant length.

2. An electron velocity modulation device comprising a cavitygresonator arranged for interaction between the electromagnetic iield contained therein and a stream of electrons entering therein, a resonant lengthof rectangular waveguidecoupled to the cavity resonator, a rectangular v waveguide feeder coupled to the resonant length of rectangular waveguide,` a symmetrical inductive coupling diaphragm extending into thewaveguide and positioned across the junction of said two waveguide portions, a rod of dielectric material having one end positioned within the waveguidefeeder and the other end projecting through the vdiaphragm into the resonant length, and means for adjusting the amount ofy penetration of the rod into the resonant length. Y v

3. An electron velocity modulation device as claimed in claim 2, in which the resonant length of waveguide comprisesa section of tapering height communicating at its narrow end with the cavity resonator through an aperture in the wall of the cavity resonator and a section of uniform dimensions joined to the tapering section, an aperi- Y odic hermetically sealed waveguide Window positioned between said tapered and uniform sections, the4 elfective `resonant: lengthV being one wavelength at the midfrequency of operation and the waveguide `window. being electrically midway along the resonant length.

4. A tuning arrangement as claimed in `claim 1 in which the mean amount of penetration of the rod into the`r resonant length is one eighth of the guide wavelength.

5. A tuning arrangement as claimed in claim 1 further comprising means for adjusting the coupling between Vthe resonator `and thef waveguide feeder simultaneously Vwith the tuning, in which means the portion of the rod penetrating into the resonant lengt-his of non-uniform height between the broad sides of the guide. Y

6. Apparatus as claimed in claim l in which the rod is at least one guide wavelength long, is of rectangular crosssection and, towards the end remote from the length of the resonant waveguide has a height which tapers uniformly to a minimum at that end.

7. Apparatus as claimed in claim 6 comprising means for supporting the rod through a longitudinally extending slot in the broad side of the waveguide feeder and a tuning control Yacting on the support means for adjusting the axial position of the rod.

8. Apparatus as claimed in claim 7 comprising a rider arranged about the waveguide feeder `for axial movement by the said tuning control and supporting the said rod of dielectric material.

9. AV tuning arrangement for adjusting the resonant frequency of a length of hollow waveguide coupled to an aperiodic length of waveguide, comprising an inductive coupling diaphragm positioned at the junction of said two lengths and a rod Iof dielectric material positioned for projection through the diaphragm into the resonant length of waveguide by an adjustable amount, the other end of the rod lying within the aperiodic length of waveguide.

10. An electron velocity modulation device having a cavityY resonator arranged for interaction Ibetween the electromagnetic field contained therein and a stream of electrons entering therein, ak resonant length of hollow kwaveguide coupled to the cavity resonator, a waveguide feeder coupled lto the resonant` length of waveguide, an inductive coupling diaphragm extending into the waveguide and positioned across the junction of said two lengths and a rod of dielectric material ,mounted for longitudinal movement within the waveguide feeder in such manner that an end projects an adjustable distance through the diaphragm into the resonant length of waveguide, the remaining portion lying Within the waveguide feeder.

11. An electron velocity modulation device as claimed in claim l0 wherein the rod ismounted on lugs projecting through a longitudinal slot in the wall of the waveguide feeder, the lugs being supported externally of the feeder.

l2. A device as claimed in claim 11 wherein the lugs are `supported in a rider encompassing the feeder, the rider [being spring-loaded and ,a micrometer screw controlling movement of said rider.

13. A device as claimed in claim 12 wherein the end of the rod remote fromthe diaphragm is tapered` in cross sectional area to reduce the discontinuity at that end.

14. A device as claimed in claim 10 wherein the resonant length of waveguide and the waveguide feeder, respectively, are of rectangular cross-section and the rod is of rectangular cross-section having over the length of rod wherein the cross-section is uniform, a height in the direction of the electric vector equal substantially to one half the height of the waveguide.

15. A device as claimed in claim 10 wherein, over the lengthof rod which projects into the resonant length of waveguide, the cross-section of the rod -is tapered to vary the degree of coupling between the resonant length of waveguide .and .theA waveguide feeder with ,the tuning of 'the device.

References Cited bythe Examiner I UNITED STATES PATENTS 2,548,816 4/51 Preston 334--41 X 2,658,147 11/53 Bainbridge S15-5.46 X 2,993,140 7/6'1 Westbrook 315-542 3,016,501 Y 1/62 Gardner et al 315-553 X 3,080,540 3/63 McFarland 333`81 GEORGE N; WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner, 

1. A TUNING ARRANGEMENT FOR A RESONANT LENGTH OF HOLLOW RECTANGULAR WAVELENGTH COUPLED TO AN APERIODIC RECTANGULAR WAVEGUIDE FEEDER COMPRISING AN INDUCTIVE COUPLING DIAPHRAGM EXTENDING SYMMETRICALLY INTO THE WAVEGUIDE AND POSITIONED ACROSS THE JUNCTION OF THE TWO WAVEGUIDE SECTION, A ROD OF DIELECTRIC MATERIAL HAVING ONE END POSITIONED WITHIN SAID FEEDER AND THE OTHER END PROJECTING THROUGH THE DIAPHRAGM INTO SAID RESONANT LENGTH AND MEANS FOR ADJUSTING THE AMOUNT OF PENETRATION OF THE ROD INTO THE RESONANT LENGTH. 